A fuel cell is an electromechanical device that produces electrical current from chemical reactions. The essential form of a fuel cell includes an ion-conducting electrolyte between two electrodes that are backed by fuel and oxidant flow distributors. A catalyst on one electrode, i.e. the anode, promotes separation of ions and electrons at the fuel side. It is only the ions that pass through the electrolyte which then at the oxidant site, i.e. the cathode, recombine with electrons. The electrons are conducted through an external circuit therewith supplying electrical power. Excellent overviews of fuel cell technology can be obtained from the following references:    “Fuel Cell Systems Explained” edited by J. Larminie and A. Dicks and published by John Wiley and Sons (2000) or in a book entitled “Fuel Cell Technology Handbook” edited by G. Hooger and published by CRC Press (2003);    Related exemplary teachings can be found in U.S. Pat. No. 5,641,586, issued to Wilson, Jun. 24, 1997, titled “FUEL CELL WITH INTERDIGITATED POROUS FLOW-FIELD”;    U.S. Pat. No. 5,683,828, issued to Spear et al., Nov. 4, 1997, titled “METAL PLATELET FUEL CELLS PRODUCTION AND OPERATION METHODS”;    S. J. Lee, S. W. Cha, Y. C. Liu, R. O'Hayre, F. B. Prinz, “High Power-Density Polymer-Electrolyte Fuel Cells by Microfabrication”, in Micro Power Sources, K. Zaghib and S. Surampudi (eds.), Proceedings, V. 2000-3, The Electrochemical Society Proceeding Series, Pennington, N.J., 2000;    S. J. Lee, S. W. Cha, R. O'Hayre, A. Chang-Chien, F. B. Prinz, “Miniature Fuel Cells with Non-Planar Interface by Microfabrication”, in Power Sources for the New Millennium, M. Jain, M. A. Ryan, S. Surampudi, R. A. Marsh, and G. Nagarajan (eds.), Proceedings, V. 2000-22, The Electrochemical Society Proceeding Series, Pennington, N.J., 2000;    R. O'Hayre, T. Fabian, S. J. Lee, F. B. Prinz, “Lateral Ionic Conduction in Planar Array Fuel Cells”, Journal of the Electrochemical Society, Volume 150, Number 4, April 2003, pp. A430-A438; and    S. J. Lee, A. Chang-Chien, S. W. Cha, R. O'Hayre, Y. I. Park, Y. Saito, F. B. Prinz, “Design and Fabrication of a Micro Fuel Cell Array with ‘Flip-Flop’ Interconnection”, Journal of Power Sources, Volume 112, Issue 2, November 2002, pp. 410-418.
Prior art FIG. 1 shows a cross-section side view of a conventional fuel cell assembly. The assembly includes a membrane electrolyte 9 with catalyst-loaded gas diffusion layer 2 on either major face of membrane electrolyte 9. The primary electrochemical reaction occurs at the interface between membrane electrolyte 9 and its adjacent catalyst-loaded gas diffusion layer 2. The membrane-electrode assembly is interposed between two backing layers 30. Backing layers 3 are manufactured to allow for open passages 31 for reactant flow. The open passages in conventional fuel cells are either parallel or serially arranged distribution channels that distribute the reactant fluid along the gas diffusion layer 2. For optimum operation it is desirable to distribute the reactant fluid as evenly as possible with minimal pressure and flow variances while keeping the design space for the distribution channels to a minimum. The present invention addresses this need.
In order to keep the different components together and isolate reactants at either side of membrane electrolyte 9, prior art fuel cells employ a mechanical clamping structure that may include threaded fasteners 4 such as bolts and/or nuts and other well-known mechanical clamping elements such as plates 41 and the like. In prior art fuel cells, the mechanical compression of the fuel cell's core structure within the inner boundaries of a surrounding elastomer gasket 5 may influence the fuel cell's efficiency. It is noted that the elastomer gasket 5 is positioned between the membrane electrolyte 9 and backing layers to isolate reactants on either side of membrane electrolyte 9. Consequently, the mechanical structure involved for providing the required compressive force and for evenly distributing that compressive force across the fuel cell's core structure increases the fuel cell's over all size, complexity and fabrication cost.
An alternative approach has been introduced in the prior art to keep the different components together and to isolate reactants at either side of membrane electrolyte 1 without relying on a clamping mechanism. In this alternate approach pure adhesives are used. However, bonding of a membrane electrolyte with pure adhesives introduces severe assembly challenges due to compatibility issues between the membrane electrolyte and the pure adhesive. Furthermore, pure adhesives are known to fail readily when subject to expansion of the membrane electrolyte as well as varying degrees of moisture content. Accordingly, there is a need in the art for a fuel cell assembly that may be efficiently fabricated and operated without need of a mechanical clamping structure and that takes into account the limitations of pure adhesives used for bonding fuel cell elements. The present invention addresses this needs.